U.S. patent application number 13/880202 was filed with the patent office on 2013-08-15 for long-life metal sliding contacts.
The applicant listed for this patent is Nicolas Argibay, Wallace Gregory Sawyer. Invention is credited to Nicolas Argibay, Wallace Gregory Sawyer.
Application Number | 20130210243 13/880202 |
Document ID | / |
Family ID | 46207639 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130210243 |
Kind Code |
A1 |
Argibay; Nicolas ; et
al. |
August 15, 2013 |
LONG-LIFE METAL SLIDING CONTACTS
Abstract
In one embodiment, a sliding contact system includes a first
metal contact, a second metal contact in sliding engagement with
the first contact, and a lubricant in which the first metal contact
and the second metal contact are immersed to inhibit oxidation and
cold welding of the contacts.
Inventors: |
Argibay; Nicolas;
(Albuquerque, NM) ; Sawyer; Wallace Gregory;
(Gainesville, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Argibay; Nicolas
Sawyer; Wallace Gregory |
Albuquerque
Gainesville |
NM
FL |
US
US |
|
|
Family ID: |
46207639 |
Appl. No.: |
13/880202 |
Filed: |
October 26, 2011 |
PCT Filed: |
October 26, 2011 |
PCT NO: |
PCT/US11/57815 |
371 Date: |
April 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61406769 |
Oct 26, 2010 |
|
|
|
Current U.S.
Class: |
439/3 ;
427/435 |
Current CPC
Class: |
H01R 43/00 20130101;
H02K 13/00 20130101; H01R 39/56 20130101; H01R 39/24 20130101; Y02E
10/725 20130101; H02K 9/28 20130101; H01R 39/22 20130101; Y02E
10/72 20130101; H01R 39/46 20130101; H01R 39/00 20130101 |
Class at
Publication: |
439/3 ;
427/435 |
International
Class: |
H01R 39/00 20060101
H01R039/00; H01R 43/00 20060101 H01R043/00 |
Goverment Interests
STATEMENT OF GOVERNMENTAL SUPPORT
[0002] This invention was made with government support under grant
number N00014-09-1-0584, awarded by the Office of Naval Research of
the United States government. The government has rights in the
invention.
Claims
1. A sliding contact system comprising: a first metal contact; a
second metal contact in sliding engagement with the first contact;
and a lubricant in which the first metal contact and the second
metal contact are immersed to inhibit oxidation and cold welding of
the contacts.
2. The sliding contact system of claim 1, wherein the first metal
contact is a solid member.
3. The sliding contact system of claim 1, wherein the first metal
contact is a commutator.
4. The sliding contact system of claim 1, wherein the first metal
contact is a slip ring.
5. The sliding contact system of claim 1, wherein the second metal
contact comprises a plurality of metal bristles.
6. The sliding contact system of claim 5, wherein the second metal
contact is harder than the first metal contact.
7. The sliding contact system of claim 1, wherein the lubricant
comprises one or more of a fluorinated liquid and an alcohol.
8. The sliding contact system of claim 1, wherein the lubricant
comprises a fluorinated liquid.
9. The sliding contact system of claim 1, wherein the lubricant
comprises a hydrofluoroether.
10. The sliding contact system of claim 1, wherein the lubricant
comprises a liquid lubricant in which the contacts are
submerged.
11. The sliding contact system of claim 1, wherein the lubricant
comprises a saturated gas that contains lubricant that condenses on
the surfaces of the contacts.
12. The sliding contact system of claim 11, wherein the gas is an
inert gas that contains no oxygen.
13. The sliding contact system of claim 1, further comprising a
sealed casing or housing that prevents escape and evaporation of
the lubricant to the atmosphere.
14. A method of reducing wear of metal sliding contacts, the method
comprising: immersing the metal sliding contacts in a lubricant
that prevents oxygen from reaching the contacts, inhibits
oxidation, and inhibits cold welding of the contacts.
15. The method of claim 14, wherein immersing the metal sliding
contacts comprises submerging the contacts in a liquid
lubricant.
16. The method of claim 14, wherein immersing the metal sliding
contacts comprises immersing the contacts in a gas that is
saturated with the lubricant that condenses on the contacts.
17. The method of claim 14, wherein immersing the metal sliding
contacts comprises immersing the contacts in a lubricant that
comprises one or more of a fluorinated liquid and an alcohol.
18. The method of claim 14, wherein immersing the metal sliding
contacts comprises immersing the contacts in a fluorinated
liquid.
19. The method of claim 14, wherein immersing the metal sliding
contacts comprises immersing the contacts in a hydrofluoroether.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to co-pending U.S.
Provisional Application Ser. No. 61/406,769, filed Oct. 26, 2010,
which is hereby incorporated by reference herein in its
entirety.
BACKGROUND
[0003] Sliding contacts are used in various applications, including
motors and generators. Such contacts often comprise a first,
stationary contact and a second, rotating contact that is
maintained in sliding engagement with the first contact as the
second contact rotates relative to the first contact. Because
sliding contacts make physical contact with each other during use,
contact wear can be a problem. This is particularly true when
higher currents are passed through the contacts. Due to such wear
issues, most sliding contacts comprise a metal contact and a
graphite brush that brushes across the surface of the metal.
Because graphite has a low coefficient of friction, wear is
reduced. Conventional graphite and electrographite brushes are not
effective above a current density threshold where ohmic heat losses
become unmanageable due to the intrinsic bulk resistivity and
thermal transport characteristics of these materials. When a
graphite brush achieves high temperature due to excessive current
density, the threshold being a function of geometry, composition,
and environment, water is desorbed from the brush causing
catastrophic wear of the brush resulting in system failure. In
contrast, metal on metal sliding contacts can be used to pass much
higher currents. Therefore, metal on metal sliding contacts would
be preferable if it were not for the above-mentioned wear
problems.
[0004] In view of the above discussion, it can be appreciated that
it would be desirable to have metal on metal sliding contacts that
are less susceptible to wear.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The disclosed systems and methods can be better understood
with reference to the following drawings. The components in the
drawings are not necessarily to scale.
[0006] FIG. 1 is a schematic partial side view of a first
embodiment of a metal sliding contact system.
[0007] FIG. 2 is a schematic partial side view of a second
embodiment of a metal sliding contact system.
[0008] FIG. 3 is a graph that plots wear rates observed in
experiments.
[0009] FIG. 4 is a schematic side view of an embodiment of a motor
that incorporates a metal sliding contact system.
[0010] FIG. 5 is a schematic end view of an embodiment of a
generator that incorporates a metal sliding contact system.
DETAILED DESCRIPTION
[0011] As described above, it is desirable to use all metal
contacts in motors, generators, and other applications where
sliding contacts are needed because a greater current density may
be passed through such contacts than through graphite on metal
contacts.
[0012] Unfortunately, metal on metal sliding contacts tend to
suffer from increased wear when used to deliver high amounts of
current due to susceptibility for electrochemically enhanced
corrosion. It has been determined that the high wear rates observed
with metal on metal sliding contacts are, in significant part,
caused by corrosion of the contacts. It has therefore been
determined that the wear rates of metal on metal sliding contacts
can be significantly reduced by reducing such corrosion. In sliding
contacts embodiments described below, corrosion is reduced by
reducing exposure of the contacts to oxygen. In some embodiments,
this is achieved by immersing the contacts in a fluid that prevents
oxygen from reaching the contacts. In some embodiments, the fluid
is a liquid lubricant or a gas that is saturated with a lubricant
that condenses on the contacts.
[0013] When metal contacts are exposed to air, the exposed surfaces
of the contacts form oxide. Although the oxide can be beneficial
from the standpoint of preventing welding of two otherwise bare
metal surfaces, a phenomenon referred to as cold-welding, oxidation
can lead to subsurface fatigue cracks that can result in
delamination and the formation of debris particles, which is the
primary wear mechanism in low wear metal sliding electrical contact
applications. This wear mechanism is more pronounced when higher
currents are used because of the effect of the strong
electromagnetic fields that are generated by relatively high
current transport, by accelerating electrochemical corrosion in the
vicinity of the sliding interface. If oxidation can be reduced,
however, such delamination can be reduced, vastly increasing the
life of the contact.
[0014] Although oxidation can be prevented or reduced by simply
removing oxygen from the environment in which the contacts are
used, the lack of oxidation can lead to cold welding. In
particular, the pure metal-to-metal contact that occurs without
such oxidation, in combination with increased temperatures
resulting from the high current passed and the friction generated,
can cause the contacts to melt and weld to each other. Desirable
results can be achieved, however, when oxidation is inhibited to
reduce wear and lubrication is provided to prevent cold welding. It
has been determined that a metal-metal sliding contact system
having improved wear characteristics can be obtained by immersing
the contacts in a lubricant that both reduces friction between the
contacts and reduces oxidation of the contacts. Example embodiments
of such systems are described below.
[0015] FIG. 1 illustrates a first example sliding contact system
10. As indicated in that figure, the system 10 comprises a first
contact 12 that engages a second contact 14. One or both of the
contacts 12, 14 is moved (e.g., rotated) such that the two contacts
slide relative to each other while in physical contact (i.e.,
sliding engagement). In the example of FIG. 1, the first contact 12
comprises a solid member having an outer surface 16. In some
embodiments, the first contact 12 comprises a cylindrical element,
such as a commutator or slip ring. As is also illustrated in FIG.
1, the second contact 14 is formed as a brush having multiple
bristles 18 that engage the outer surface 16. The contacts 12, 14
are provided within an airtight, sealed casing or housing (not
shown) that prevents escape and/or evaporation of a lubricant
(described below) present within the system 10.
[0016] Irrespective of their particular configurations, the
contacts 12, 14 are both metal contacts. Suitable metals comprise
any metal or metal alloy that is highly conductive but that may
oxidize and therefore may be susceptible to increased wear when
high current is passed through it. Example metals include copper,
iron, aluminum, silver, nickel, molybdenum, tin, and other metals
that can be added to those metals to form metal alloys (e.g.,
brass, bronze, and steel). In some embodiments, the metals are
selected such that the second contact 14 (i.e., brush contact) is
significantly harder than the first contact 12. In such a case,
wear is "shifted" from the contact that is most susceptible to wear
(i.e., the second contact 14 with its narrow bristles 18) to the
contact that is less susceptible to wear (i.e., the first contact
12 with its greater thickness and larger mass of material). In one
example embodiment, the first contact 12 is made of copper and the
second contact 14 (i.e., the bristles 18) are made of beryllium
copper, which is much harder than pure copper. In another example
embodiment, the first contact 12 is made of copper and the bristles
18 of the second contact 14 is made of steel, which is also much
harder than copper. In a further example embodiment, the first
contact 12 is made of copper and the second contact 14 is made of
hardened brass, which is much harder than copper. In a yet another
example embodiment, the first contact 12 is made of copper and the
second contact 14 is made of argentium silver, which is likewise
much harder than copper. These are just but a few examples of
metals and metal pairings that can be used.
[0017] With further regard to FIG. 1, at least the portions of the
contacts 12, 14 that come into engagement with each other are
immersed in a lubricant 20. In the embodiment illustrated in that
figure, the contact areas of the contacts 12, 14 are submerged in a
liquid lubricant. As indicated in FIG. 1, the lubricant 20 can
comprise a pool of liquid that is covered with a gas 22. In some
embodiments, the gas 22 comprises air. In other embodiments, the
gas 22 comprises an inert gas other than oxygen, such as helium,
argon, or nitrogen. In alternative embodiments, the system 10 can
be completely filled with the lubricant 20 such that little or no
gas is within the sealed casing or housing that contains the
system.
[0018] The lubricant 20 can comprise any liquid that reduces
friction between the contacts 12, 14, cools the contacts to prevent
metal-to-metal welding, and inhibits oxidation. In some
embodiments, the lubricant 20 comprises a fluorinated liquid or an
alcohol. Example fluorinated liquids include hydrofluoroether
solutions (e.g., Novec 7500 by 3M Corp.). Example alcohols include
ethanol and propanol solutions.
[0019] Because a liquid lubricant can create drag, it is possible
that submersion of the contacts will limit the speed at which
equipment in which the contacts are used (e.g., motor or generator)
can be operated. In such cases, it may be preferable to provide the
lubricant in the form of a saturated gas. Such an embodiment is
illustrated in FIG. 2. The sliding contact system 30 of FIG. 2 is
similar in many ways to the system 10 of FIG. 1. Therefore, the
system 30 comprises a first metal contact 12 that engages a second
metal contact 14 having a plurality of bristles 18. In addition,
the contacts 12, 14 are immersed in a lubricant. In this case,
however, the lubricant comprises a gas 32 that is saturated with a
liquid lubricant. The gas 32 can be an inert gas that contains no
oxygen. By way of example, the gas can be helium, argon, or
nitrogen gas. The lubricant can comprise any of the lubricants
identified above. In such a case, the liquid lubricant contained in
the gas 32 condenses on one or both of the contacts 12, 14 to
provide the desired lubrication and oxidation inhibition. In some
embodiments, condensation can be facilitated by cooling one or both
of the contacts 12, 14. For example, the contact 12 can be cooled
by delivering cooling water or another fluid through one or more
passages 34 formed beneath the surface 16 of the contact or in
another location. Irrespective of how the condensation occurs, the
lubricant that condenses on the contact(s) reduces friction and
inhibits oxidation. Because a much smaller volume of liquid
lubricant is present, however, drag is reduced and greater
operating speeds are possible.
[0020] Testing was performed to confirm that systems such as those
described above can reduce wear in metal-metal sliding contacts. In
that testing, a copper-beryllium fiber was pressed against a
rotating copper disc. In each experiment, the fiber had a diameter
of approximately 120 microns (.mu.m), and a bend radius of
approximate 3 millimeters (mm). The fiber was pressed against the
disc with a force of approximately 0.5 newtons (N) and the disc was
rotated at a speed of approximately 10 mm/second. The contacts were
independently submersed in hydrogen peroxide, water, and a
hydrofluoroether. As can be appreciated from the graph of FIG. 3,
significantly less wear resulted when the hydrofluorether was used
to lubricate the contacts.
[0021] FIG. 4 illustrates an example component that incorporates a
sliding contact system of the type described above. More
particularly, FIG. 4 illustrates a motor 40, such as a brushed DC
motor, that incorporates a sliding contact system. As shown in FIG.
4, the motor 40 includes an outer housing 42 that houses an
armature 44 that is mounted to a central shaft 46. Surrounding the
armature 44 are stator magnets 47 (only one magnet visible in FIG.
4).
[0022] The motor 40 further comprises a sealed compartment 48 that
contains a commutator 50, which is also mounted to the shaft 46.
The compartment 48 is sealed around the shaft 46 with airtight
bearings 52. Also provided within the compartment 48 are brushes 54
that include bristles 56 that make physical contact the outer
surface of the commutator 50 while it rotates with the shaft. In
such an arrangement, the commutator 50 can be considered to
comprise a first contact and the brushes 54 can be considered to
comprise second contacts.
[0023] To reduce wear of the commutator 50 and the brushes 54, the
commutator and brushes are immersed in a fluid 58 that prevents
oxygen from reaching the contacts. In some embodiments, the fluid
is a liquid lubricant or a gas that is saturated with a lubricant
that can condense on the contacts.
[0024] FIG. 5 illustrates a further example component that
incorporates a sliding contact system of the type described above.
More particularly, FIG. 5 illustrates a generator 60, such as a
generator that could be used in a wind turbine. As shown in FIG. 5,
the generator 60 includes an outer housing 62 that houses slip
rings 64 (only one slip ring visible). Positioned within the slip
rings 64 is a contact element 66 that supports multiple brushes 68
that each comprise multiple bristles 70, which make contact with
the slip rings. In such an arrangement, the slip rings 64 can be
considered to comprise first contacts and the brushes 68 can be
considered to comprise second contacts.
[0025] The space between the slip rings 64 and the contact element
66 is sealed and contains a fluid 72 that prevents oxygen from
reaching the contacts. In some embodiments, the fluid is a liquid
lubricant or a gas that is saturated with a lubricant that can
condense on the contacts.
[0026] Although various embodiments have been described above, it
is to be understood that alternative embodiments are possible. The
present disclosure is intended to extend to all such embodiments.
For example, in further embodiments, an additive, such as acetic
acid, can be added to the lubricant to remove corrosion that may
form on the contacts.
* * * * *